Reliance on external sources of energy is a continuing source of national concern. Accordingly, the government has mandated that manufacturers improve the efficiency of their air handlers. To this end, the government through the Department of Energy recently supported a two year study by GE Global Research (DOE Award DE FC26-000T40993, and principal author, Herman Wiegman), with the goal of improving the efficiency of furnace blowers. This project known as the “Advanced Blower Project” had a total spending budget of 3.2 million dollars. One of the issues studied involved air flow control through the blower housing.
Traditionally, blower housings for residential and commercial air handlers and hot air furnaces have been fabricated from sheet metal, and involve a design that has changed very little over the past several decades. The shape involves a modified cylinder having curving walls attached to planar front and back walls. The blower motor is mounted with its central axis along the central axis of the cylinder. The cylinder opens into an air exhaust shaped like a rectangular bell from a French horn and which includes an elongated channel that extends across the length of the cylinder parallel to the central axis. This design involves curving right angle edges that require considerable bending and welding during fabrication of the sheet metal. This leads to the possibility of injury to workers who are exposed to sharp edges, and extreme heat in welding. In addition, there are often functional features such as mounting flanges and clamps that need to be individually worked and/or attached to the blower housing. The final assembly of the blower requires intensive labor and puts the assembly worker at risk of injury through cuts or burns. This adds considerable expense to the fabrication of the housing.
Despite the manufacturing difficulties that metal presents, it has always been the material accepted by the industry for this component because of the environment that the blower encounters during use. The blower is generally located at the bottom of the furnace, below the heater, or in the central section of an air heater which could include a series of heating coils that may reach temperatures of about 1,000° F. While there is often a partition and insulation between the blower and the heater, the temperatures to which the blower housing are subjected can be quite high. In particular this is true for some spots, such as at the air exhaust. In addition to the stress of elevated temperatures, the environment can be corrosive, and as some furnaces are located outside residences, they can also be subjected to cold temperatures. The blower housing also needs to have sufficiently high mechanical properties, since one of the industry tests is a drop test in which the furnace is dropped, and the blower housing must survive intact. Finally, the blower housing tunnels relatively large volumes of air. It may run continuously in cold weather, and is housed in a furnace cabinet that is often a large sheet metal box that can actually act to amplify the sound, if not sufficiently dampened for sound transmission. An example of a furnace set up is shown in U.S. Pat. No. 5,375,586 to Schumacher et al., while an example of an improvement in blower housings is shown in U.S. Pat. No. 6,324,894 to Gatley, Jr.
Molded polymeric housings present many advantages over the prior art metal housings. They significantly reduce the potential for injury during assembly by eliminating the need for high temperature welding operations, and for cutting and bending sheet metal. They greatly increase the efficiency of assembly by providing the opportunity for integrally molded functional elements, such as mating clamps and mounting flanges. Thus, molded polymeric housings have been in use for a significant period of time for blowers for air conditioners, and in particular room air conditioners. In addition, they have been used for small scale heating blowers subjected to relatively low temperatures, such as hair dryers. These applications often involve the use of very expensive compositions, which can be used since the size is small. Other hot air furnace components, such as the condensate pan, have been made of molded resins for some time.
However, despite the use of molded polymerics for these other applications and for housings in window air conditioners for well over 30 years, the HVAC industry has failed to capitalize on the many advantages which could be realized through the use of molded polymeric blower housings for hot air furnaces. There are several reasons to account for the prior art practice, including the belief that the blower environment is better suited for metal, which has proven longevity and fire resistance. An additional problem is the lack of understanding in the compounding industry of how to achieve sufficient structural reinforcement, such as through the use of glass fiber reinforcement, while maintaining proper sound dampening properties for this application.
The present invention provides the solution to the previously mentioned issues, while also presenting a platform for improved air flow efficiencies. The present invention provides a molded composite compound blower housing for hot air furnaces. This blower housing includes integral molded functional parts, such as mating clamps, and mounting flanges. It has the desired mechanical properties including tensile and impact properties at the necessary operating temperature range. It can be molded into complex curving configurations and surface characteristics derived by computer modeled images to maximize flow conditions. It does this while maintaining quiet and safe operating conditions.